Advanced computer systems are being developed with a point-to-point (PTP) interconnect technology between processors such as central processing units (CPUs) and between CPUs and an input/output (I/O) hub (IOH) for speed, performance and scalability.
For such systems, where there is no snoop filter in any CPU node, a requesting node (e.g., a processor node) that wants to have ownership of a cache line address needs to broadcast the snoop to all nodes in the system and collect all snoop responses before the cache line ownership can be granted to the requesting node. For a broadcast snoop, the IOH node would normally be the last one to return a snoop response (since the IOH core runs at a much slower clock than a CPU core). This slower IOH snoop response has a negative impact on performance, since cache line ownership cannot be decided until all snoops are received, therefore blocking other requests targeting the same cache line and blocking the request from being evicted to make room for a new request.